Carb Rebuild Problems

duckrock

Member
I have a 740 that started running horrible and then started leaking fuel from air inlet. Decided I'd attempt the rebuild since my mechanic was swamped. Everything came apart fine
and cleaned up nice. Bought a TSC kit (I know) and float. First attempt after reinstalling on tractor i didn't get any fuel into carb. Found the new valve and seat would stick
closed. I cleaned and reused old valve and seat (spring type). Second attempt the tractor start but I couldn't get the RPMs to come down. I had more throttle response using the
choke than I did with the throttle lever. Then I remembered I had the required "extra" new parts - a white felt and rubber bushing left over in the kit. Sprayed some carb cleaner
around throttle shaft and RPMs went up. Guessing I had an air leak I read the shop manual again then removed carb and put the rubber bushing on the throttle shaft and the felt
bushing on the choke shaft. Third attempt to start the tractor will fire up, run at high RPMs, then stall with it choked, but it won't stay running. This is why I don't like dealing
with the carb, but they seem so simple. Also, I have already cleaned the air cleaner and filled with new oil.

Could someone provide some guidance/suggestions? I have the shop and repair manuals but still can't figure it out.
 
If you don't already have a fire extinguisher within arm's reach,get one before doing anything else. A backfire can easily set you,the tractor and building afire. The original problem of fuel running out of intake is classic needle/seat/float/trash symptom. Since you have re-installed old parts,that might still be the problem. Before tearing into it again,try this. Remove drain plug from carb bowl and hold a 1 quart or larger container to catch fuel. You should see a steady stream. If stream stop's or become's smaller,disconnect fuel line from carb to see if stream keep's running without interruption. If stream is good without interruption,check for clogged filter at carb inlet and/or bad needle & seat. If stream from line stop's or is interrupted,you need to drain the tank and remove the valve-bowl assembly for cleaning or replacement.
 
Couple of comments/questions:
As the other reply said, the old needle valve and seat might have been your original problem, probably you shouldn't re-use them. With the new needle and seat and float installed, holding the assembly in normal horizontal position you should be able to move the float up and down freely to open/close. If not or it's sticking, you need to find out why and correct that or get another set. Also, when you removed the throttle linkage is there any chance that you knocked off the governor rod connection? Check that and the spring. You can have a little (vacuum) leakage around the throttle shaft and it can upset the calibration of the carb a bit, but I wouldn't think it would cause the engine to race. Also, if you had gas leaking from the carb air intake, you better make sure you didn't get fuel contamination in your crankcase oil. That can happen over time if the carb leaks gas into the engine by gravity flow. -Will
 
I keep having a problem with the needle sticking myself. I can hold it up with the bowl off, push the float up and needle sticks when it wants to. Anyone out there have an all brass needle? OP, if your float assembly hangs up on the sides of the bowl that will cause problems. I wouldnt try that yet because you might mess them up. They are a pretty close fit and its hard to tell if they are hanging up. Did you clean your screen and put it back right? It has a little square hole in one side.
 
I'm pretty sure I don't have a fuel flow problem. It was running good at high RPM just wouldn't idle down. The starting and cutting out problem started after I installed the bushings I forgot on the choke and throttle shaft. Fuel flows out the drain just fine.
 
Pulled carb off this morning to check that I had the throttle shaft/valve installed correctly based on someone's suggestion outside of DB. It was in correctly and when I bolted carb back up it stayed running. I did run it without the governor linkage attached and was able to get idle down if i pushed idle screw against the stop. Still won't idle down and run as smooth as some of my other tractors. Starting to think maybe I have other issues too. Possibly timing but I can't see the timing marks in the window because of the frame/hydro pump. Also wondering if governor linkage needs to be readjusted after a carb rebuild? Any other ideas/things I should look at?
 
I would definitely go through the governor linkage adjustment procedure in the service manual based on your description so far. But I still wouldn't rule out a vacuum leak somewhere.
 
Went out to play with carb last night and found I left the gas on. Once again gas was flooding carb. I switched to the new needle and seat. Think it sticks closed but was able to get tractor to idle down closer to where it should be. So for now things are on hold while I wait for a new needle and seat to show up in mail box.
 

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